Problem: How many significant figures does $0.0421940$ have?
Explanation: Identify the non-zero digits and any zeros between them. These are all significant. $0.0{42194}0$ Leading zeros are not significant. $\color{orange}{0.0}{42194}0$ Since there is a decimal, trailing zeros are significant. $\color{orange}{0.0}{421940}$ Counting all the significant digits gives us 6.